The present invention is directed generally to air dryers, and more particularly to an air filter dryer for use in a compressed air systems for filtering oil particles and for removing moisture from a stream of compressed air.
Compressed air systems with which the invention might be utilized may be found in a variety of manufacturing and assembly plants. For example, such systems are used with pneumatically operated tools and pneumatically controlled machines. These tools and machines are subject to substantial impairment in the event of corrosion caused by the presence of moisture in the compressed air system. As a further example, such compressed air systems are used in the operation of sensitive pneumatic instruments and controls, which may be materially adversely affected by excessive moisture in the compressed air stream. In addition to moisture, the compressed air stream may also contain impurities and contaminants such as oil, dust, pipe scale and other particulate matter, which can and do produce harmful results upon condensation of the water vapor.
Numerous forms of air dryers have been proposed and are presently in use. One example is a refrigerated air dryer. In this type of dryer, the hot compressed air is brought into contact with a refrigeration coil to lower air temperature and cause the water vapor to condense. The condensate is then collected in a moisture separator. While this type of air dryer has been found to be quite effective for removing moisture from compressed air, there still remains room for improvement. For example, this type of system requires a two-stage process. First, the air must be cooled, then the vapor produced from cooling the air must be separated. The cooling unit and the moisture separator are usually connected by lengths of tubing, which requires that the compressed air travel some distance to the separator. Consequently, some of the water vapor is often re-evaporated into the cooled air. As a result, at least some of the moisture remains in the air which is utilized by the pneumatically controlled machinery. This, of course, is undesirable.
Another form of filter dryer is the adsorbent type of air dryer which employs a large tank or chamber within which a desiccant is stored. The compressed air is passed through the tank prior to being supplied to the air supply line for the tools or instruments, such that the desiccant adsorbs a considerable amount of vapor. However, the desiccant eventually reaches a saturation point, at which time the filter-dryer is no longer useful. Therefore, the operating and recharging costs of this type of filter are often high.